This invention is directed generally to a tool and related method for aligning a pair of similar pipe flanges at opposite ends of a length of pipe.
Individual lengths of pipe are generally joined together or to other apparatus by coupling with similar apertured flanges at respective ends thereof, using bolts or the like. These flanges are normally welded or otherwise permanently affixed to the two ends of a length of pipe. Hence, ease of coupling together a plurality of aligned lengths of pipe requires that the bolt holes in the flanges of each of the pipes to be joined be in alignment. However, the flanges are normally neither applied to the pipes in the field nor adjustable with respect to the pipes in the field. Hence, to assure alignment of flange bolt holes from one length of pipe to the next, it is necessary that the flanges on each end of each length of pipe be attached thereto with their bolt holes in coaxial alignment. It will be appreciated that such alignment is also important when replacing a length of pipe in the field, as it permits ready alignment of the flanges at both ends of the replacement pipe with the respective flanges of the adjacent length of pipe to either side thereof.
The most widely used current method of bolt hole alignment is commonly referred to as "true holing" or "two holing" of the flanges. This method of alignment involves first permanently attaching a flange to one end of the pipe, inserting bolts into two adjacent bolt holes and rotating both pipe and flange until a small level supported by the bolts indicates a level position. Thereafter, a loose flange is placed on the opposite end of the pipe and a pair of bolts inserted into adjacent bolt holes of the second flange. The level is then supported on these bolts and the loose flange is rotated with the pipe remaining stationary until the level again indicates a level position. The loose flange is then permanently attached to the pipe in that position, resulting in its bolt holes being substantially coaxially aligned with the bolt holes of the first flange at the opposite end of the pipe.
While the foregoing system of alignment has been widely used for many years, it does not always result in perfect alignment and leaves some areas for improvement. For example, clearance between the bolts and bolt holes in a typical flange is sufficient to permit some tilting or cocking of each bolt with respect to its bolt hole. Often, workers will use even a smaller size of bolt for convenience in insertion through the bolt holes, which results in even a greater potential for such tilting and cocking of the bolts. Hence, with the level in the foregoing method of alignment being supported by such tilted or cocked bolts, there is no assurance that the "level" position obtained at one end of the pipe will be matched by the "level" position at the opposite end. That is, the amounts and directions of tilting or cocking of the bolts are unpredictable and hence cannot be assumed to be the same at both ends of the pipe when the foregoing procedure is followed. Once the preassembled pipe and flanges are in the field, the resulting inaccuracies can cause delays and high labor costs in installation, repair and/or replacement of pipe.